Materials, methods, and devices for siloxane contaminant removal

ABSTRACT

Adsorbent materials are disclosed, along with filter elements containing the adsorbent materials methods of using adsorbents to remove siloxane contaminants from a gas stream. The method includes providing an adsorbent material that has been washed with an acid and passing a gas through the adsorbent material so as to reduce siloxane levels in the gas. A filter element for reducing siloxane levels in a gas includes a first adsorbent material, the first adsorbent material comprising an acid-washed adsorbent; and a second adsorbent material, the second adsorbent material comprising an acid-impregnated adsorbent.

This application is being filed as a PCT International Patentapplication on Mar. 15, 2013 in the name of Donaldson Company, Inc., aU.S. national corporation, applicant for the designation of allcountries and Brian N. Hoang, a U.S. Citizen; Gerald Weineck, a U.S.Citizen; Karthik Viswanathan, an Indian Citizen; and Andrew J. Dallas, aU.S. Citizen, are inventors only for the designated states, and claimspriority to U.S. Provisional Patent Application No. 61/643,732, filedMay 7, 2012, the contents of which are herein incorporated by referencein its entirety.

FIELD OF THE INVENTION

The current technology relates to adsorbent materials.

BACKGROUND

Siloxane compounds, such as hexamethyldisiloxane,hexamethylcylotrisiloxane, and trimethylsilanol are contaminants thatcan interfere with many advanced manufacturing processes. For example,siloxane compounds can seriously damage equipment used in manufacturingof electronic components, such as photolithography equipment, includinglenses and optical components. Removal of siloxane compounds fromambient air, tool environments and point of use air streams is criticalto avoid damaging such equipment and components. Therefore, a needexists for methods and materials that can reliably remove siloxanecompounds from gases.

SUMMARY OF THE INVENTION

The present invention is directed, in part, to methods and materials forreducing siloxane contaminants in gases. Other contaminants, such asammonia and acid gases are optionally also reduced along with siloxanes.The methods comprise, in certain embodiments, utilization of anadsorbent material that has been washed with an acid. Whensiloxane-containing gases are passed through the acid washed adsorbent,the siloxane levels in the gas are reduced.

Suitable adsorbent materials include activated carbon, as well as (forexample) silica gel, activated alumina, zeolites, nanoporous supports,and combinations thereof. Typically the adsorbent is washed with astrong acid, such as nitric acid. After being treated with the strongacid, the adsorbent is generally washed with water to remove excess acidand return the adsorbent material to a more neutral pH (although theadsorbent surface still generally has a slightly acidic pH).

The methods and media can be used to remove siloxane contaminants fromambient air, as well as from clean dry air (CDA), from nitrogen gas,from rare gases, and from other gases that may contain undesirablesiloxane levels. The removal of siloxanes, even siloxanes at very lowconcentrations, can also be beneficial in various microelectronicsmanufacturing and operational processes, such as production of flatpanel displays, the production and operation of photonics devices, andthe production and operation of photovoltaic cells. The removal ofsiloxanes is often particularly important to semiconductormanufacturing, such as in photolithography processes.

In addition to the use of an acid washed adsorbent for the removal ofsiloxanes, other adsorbent materials can be used in conjunction with theacid washed adsorbent to either further remove siloxanes, to removeother contaminants, or to remove siloxanes as well as othercontaminants. The additional adsorbent material can also includeactivated carbon, as well as (for example) silica gel, activatedalumina, zeolites, nanoporous supports, and combinations thereof. In oneimplementation the additional adsorbent is impregnated with an acid,such as a strong acid. Suitable acids include, for example, phosphoricacid and citric acid. These acid impregnated adsorbents are particularlysuitable for removal of basic contaminants, such as ammonia.

Typically the two adsorbents (such as an acid washed adsorbent in whichmost acid is removed, and an acid impregnated adsorbent in whichsignificant amounts of acid remain impregnated on the media) arearranged in a filter element so that gases sequentially flow through thedifferent adsorbents. Thus, for example, in a packed-bed filter, theremay be one packed bed for a first adsorbent, and second packed bed forthe second adsorbent.

Besides the above-mentioned acid washed adsorbent for siloxane removal,and the acid impregnated adsorbent for removal of bases, other materialscan be incorporated for removing other contaminants. These materialsinclude an acid gas remover (AGR) that may comprise adsorbentimpregnated with potassium iodide (KI) or potassium carbonate (K₂C0₃) orsodium hydroxide (NaOH). This acid gas remover can also further removesiloxanes in some implementations. When combining the acid gas removerwith acid washed adsorbent, the ratio of acid washed adsorbent to acidgas remover is in some embodiments from 2:1 to 1:2; or alternativelyfrom 3:1 to 1:3; and alternatively from 10:1 to 1:10.

The invention is also directed to filter elements for reducing siloxanelevels in a gas, the filter element comprising at least two adsorbents.In some embodiments the first adsorbent material comprises anacid-washed adsorbent; and the second adsorbent material comprises anacid-impregnated adsorbent.

When acid treatment is used to modify the surface of the adsorbent tocreate an acid washed adsorbent, generally the acid treatment comprisestreating the adsorbent material or substrate with a strong acid, oftenwith an aqueous acid solution that is at least 5 percent by weight acid,more typically an aqueous acid solution that is at least 10 percentstrong acid by weight. In certain implementations the acid treatmentcomprises treatment of the substrate in an acid solution that is atleast 35 percent acid, and optionally a solution that is at least 70percent acid. In some embodiments the acid solution comprises from 5 to85 percent acid, in others the acid solution comprises from 20 to 75percent acid, and yet others the acid solution comprises from 30 to 60percent acid. Note that even greater than 85 percent acid can be added,typically by use of acid fumes or vapors.

A particularly suitable acid used for acid washing is nitric acid. Insome implementations the aqueous acid solution comprises nitric acid,optionally at least 5 percent nitric acid, more typically at least 10percent nitric acid. In certain implementations the acid solutioncomprises at least 35 percent nitric acid, and optionally at least 70percent nitric acid. In some embodiments the acid solution comprisesfrom 5 to 85 percent nitric acid, in others the acid treatment comprisesfrom 20 to 75 percent nitric acid, and in yet others the acid solutioncomprises from 30 to 60 percent nitric acid.

After acid treatment the adsorbent is generally rinsed one or more timeswith water, generally purified water, to remove most of the remainingacid from the adsorbent. In at least one embodiment, the pH of thewashed material is between 4 and 5, in others the pH is from 3.5 to 6.5;and in yet other implementations the pH is from 3 to 7, while in otherimplementations the pH is from 2 to 8.

The above summary of the present invention is not intended to describeeach discussed embodiment of the present invention. This is the purposeof the figures and the detailed description that follows.

FIGURES

The invention may be more completely understood in connection with thefollowing drawings, in which:

FIG. 1 is a perspective view of filter element made in accordance withan implementation of the invention.

FIG. 2 is a cross sectional view of a first example filter element madein accordance with an implementation of the invention.

FIG. 3 is a cross sectional view of a second example filter element madein accordance with an implementation of the invention.

FIG. 4 is a cross sectional view of a third example filter element madein accordance with an implementation of the invention.

FIG. 5 is a chart showing siloxane removal from a gas stream usingadsorbent media.

FIG. 6 is a chart showing ammonia removal from a gas stream usingadsorbent media.

FIG. 7 is a chart showing ammonia removal efficiency from a gas streamusing adsorbent media.

FIG. 8 is a chart showing hexamethyldisiloxane removal efficiency from agas stream using adsorbent media.

FIG. 9 is a chart showing total siloxane removal efficiency from a gasstream using adsorbent media.

FIG. 10 is a chart showing total ammonia removal efficiency from a gasstream using adsorbent media.

While the invention is susceptible to various modifications andalternative forms, specifics thereof have been shown by way of exampleand drawings, and will be described in detail. It should be understood,however, that the invention is not limited to the particular embodimentsdescribed. On the contrary, the intention is to cover modifications,equivalents, and alternatives falling within the spirit and scope of theinvention.

DETAILED DESCRIPTION

The present invention is directed, in part, to method and materials forreducing siloxane contaminants in gases, optionally along with thereduction of other contaminants, such as bases/basic gases andacids/acidic gases. The method comprises, in certain embodiments,utilization of an adsorbent material that has been washed with an acidto reduce siloxane levels in the gas as the gas passes through theadsorbent. The invention is also directed to filter elements forreducing siloxane levels in a gas, the filter element comprising atleast two adsorbents. The first adsorbent material comprises anacid-washed adsorbent; the second adsorbent material comprises anacid-impregnated adsorbent.

The methods and media can be used to remove siloxane contaminants fromambient air, as well as from clean dry air (CDA), nitrogen gas, and raregases. The removal of siloxanes is often particularly important tosemiconductor manufacturing, such as photolithography processes. Theremoval of siloxanes can also be important on the lithography track,metrology, and during inspection processes; as well is in othermanufacturing processes. The removal of siloxanes, even siloxanes atvery low concentrations, can also be beneficial in variousmicroelectronics manufacturing process, such as production of computerdisplays, photonics, and photovoltaics.

In addition to the use of an acid washed adsorbent for the removal ofsiloxanes, additional adsorbent materials can be used in conjunctionwith the acid washed adsorbent to either further remove siloxanes, toremove other contaminants, or to remove siloxanes as well as othercontaminants.

The invention is also directed, in part, to filtration system forreducing siloxane levels in a gas, the filtration system containing afirst filter element comprising an adsorbent material, the firstadsorbent material comprising an acid-washed adsorbent; and a secondfilter element comprising an adsorbent material, the second adsorbentmaterial comprising an acid-impregnated adsorbent. The filter system isconfigured in a series for a majority of the gas to pass through thefirst filter element and then the second filter element.

The invention is further directed, in an alternative embodiment, tofiltration system comprising a first filter element comprising anadsorbent material, the first adsorbent material comprising anacid-impregnated adsorbent; and a second filter element comprising anadsorbent material, the second adsorbent material comprising anacid-washed adsorbent. The filter system is configured in a series for amajority of the gas to pass through the first filter element and thenthe second filter element.

The invention is further directed, in part, to method of reducingsiloxane levels in a gas, method comprising providing an adsorbentmaterial that has been washed with an acid; and passing a gas throughthe adsorbent material so as to reduce siloxane levels in the gas. Theinvention is further directed, in part, to a method of reducing siloxanelevels in a gas, the method comprising providing an adsorbent materialthat has been washed with a first acid and subsequently impregnated witha second acid; and passing a gas through the adsorbent material so as toreduce siloxane levels in the gas.

Adsorbent Materials

The additional adsorbent material can also include activated carbon, aswell as silica gel, activated alumina, zeolites, nanoporous supports,and combinations thereof. In one implementation the additional adsorbentis impregnated with an acid, such as a strong acid. Suitable acidsinclude, for example, phosphoric acid and citric acid. These acidimpregnated adsorbents are particularly suitable for removal of basiccontaminants, such as ammonia.

Typically the two adsorbents (such as an acid washed adsorbent in whichmost acid is removed, and acid impregnated adsorbents in whichsignificant amounts of acid remain impregnated on the media) areconfigured so that gases sequentially flow through the differentadsorbents, as opposed to mixing of the adsorbents together. Thus, forexample in a packed-bed filter, there may be one bed for a firstadsorbent, and second packed bed for the second adsorbent.

Besides the above-mentioned acid washed adsorbent for siloxane removal,and the acid impregnated adsorbent for removal of bases, other materialscan be incorporated. These include, for example, acid gas removers thatcomprise adsorbent impregnated with bases, such as potassium iodide (KI)or potassium carbonate (K₂CO₃) or sodium hydroxide (NaOH). The acid gasremover can also further remove siloxanes. The ratio of acid washedadsorbent to acid gas remover is from 2:1 to 1:2; alternatively from 3:1to 1:3; and alternatively from 4:1 to 1:4 in various exampleembodiments.

When acid treatment is used to modify the surface of the adsorbent,generally the acid treatment comprises treating the adsorbent materialor substrate with a strong acid, often with an aqueous acid solutionthat is at least 5 percent by weight acid, more typically an aqueousacid solution that is at least 10 percent strong acid by weight. Incertain implementations the acid treatment comprises treatment of thesubstrate in an acid solution that is at least 35 percent acid, andoptionally a solution that is at least 70 percent acid. In someembodiments the acid solution comprises from 5 to 85 percent acid, inothers the acid solution comprises from 20 to 75 percent acid, and yetothers the acid solution comprises from 30 to 60 percent acid. Note thateven greater than 85 percent acid can be added, typically by use of acidfumes or vapors.

In some implementations the aqueous acid solution comprises nitric acid,optionally at least 5 percent nitric acid, more typically at least 10percent nitric acid. In certain implementations the acid solutioncomprises at least 35 percent nitric acid, and optionally at least 70percent nitric acid. In some embodiments the acid solution comprisesfrom 5 to 85 percent nitric acid, in others the acid treatment comprisesfrom 20 to 75 percent nitric acid, and in yet others the acid solutioncomprises from 30 to 60 percent nitric acid.

Several acids can be used in this process such as, for example, nitricacid, phosphoric acid and sulfuric acid. Additional acids include, forexample, citric acid and malonic acid. A single acid or a mixture, and arange of different acid concentrations, can be used. The treatmentprocess can be done at static or dynamic conditions. Static conditionsinclude, for example, soaking the adsorbent in an acid solution. Dynamicconditions include, for example, having the adsorbent mixed with theacid under stirring and/or rotary or orbital shaking.

Typically an amount of acid is used that is consistent with a particularmass-to-volume ratio of the adsorbent to the acid. Such mass-to-volumeratio depends on factors such as pore volume of the adsorbents, theorigin of the adsorbent, and the bulk density of the adsorbent, forexample, although other factors can also be relevant. Suitablevolume-to-mass (ml/g) ratios include, for example, from 0.1 to 1, from 1to 10, and from 10 to 100, in the case of activated carbon. The ratio ofvolume of acid-to-volume of pores per relative to unit mass of carboninclude from 0.01 to 1, from 1 to 10, and from 10 to 100.

When acid washing is used to modify the surface of the adsorbent,generally the acid treatment comprises treating a substrate with astrong acid, often the acid is in an aqueous solution that is at least 5percent strong acid by weight of the solution, more typically at least10 percent strong acid by weight of the solution. In certainimplementations the acid comprises at least 35 percent acid by weight ofthe solution, and optionally at least 70 percent acid by weight of thesolution. In some embodiments the acid solution comprises from 5 to 85percent acid by weight of the solution, in others the acid comprisesfrom 20 to 75 percent acid by weight of the solution, and yet others theacid comprises from 30 to 60 percent acid by weight of the solution.

Treatment time also varies based on a variety of factors that includepore volume of the adsorbents, the origin of the adsorbent, and the bulkdensity of the adsorbent. The treatment time typically varies from a fewminutes up to several days. In some implementations the surfacetreatment is up to 1 hour, in other implementations the surfacetreatment is up to 24 hours, and in yet other implementations thesurface treatment is greater than 24 hours.

In various embodiments the absorbent can be used immediately after theacid treatment. In other embodiments the adsorbent is washed with waterto remove a portion of the acid. In some such embodiments 1%-10% byweight of the acid may remain in the adsorbent, and sometimes from 1 to20% by weight. In some of those embodiments 2%-7% of the acid may remainin the adsorbent. In at least one embodiment, 3%-5% of the acid remainsin the adsorbent. The pH of the sample can be controlled by the amountof water used in the wash. In various embodiments the pH of the sampleis slightly acidic. In at least one embodiment, the pH of the sample isbetween 4 and 5, in others the pH is from 3.5 to 6.5; and in yet otherimplementations the pH is from 3 to 7, while in other implementationsthe pH is from 2 to 8. Generally the amount of acidic groups will rangefrom 0.1 to 10 mmol acidic groups per gram of carbon. In someimplementations the amount of acidic groups will range from 1.0 to 10mmol acidic groups per gram of carbon; in others from 1.0 to 5.0 mmolacidic groups per gram of carbon.

The invention is also directed, in part, to filtration system forreducing siloxane levels in a gas, the filtration system containing afirst filter element comprising an adsorbent material, the firstadsorbent material comprising an acid-washed adsorbent; and a secondfilter element comprising an adsorbent material, the second adsorbentmaterial comprising an acid-impregnated adsorbent. The filter system isconfigured in a series for a majority of the gas to pass through thefirst filter element and the second filter element.

The invention is further directed, in an alternative embodiment, tofiltration system comprising a first filter element comprising anadsorbent material, the first adsorbent material comprising anacid-impregnated adsorbent; and a second filter element comprising anadsorbent material, the second adsorbent material comprising anacid-washed adsorbent. The filter system is configured in a series for amajority of the gas to pass through the first filter element and thesecond filter element.

The invention is further directed, in part, to method of reducingsiloxane levels in a gas, method comprising providing an adsorbentmaterial that has been washed with an acid; and passing a gas throughthe adsorbent material so as to reduce siloxane levels in the gas.

The invention is further directed, in part, to a method of reducingsiloxane levels in a gas, the method comprising providing an adsorbentmaterial that has been washed with a first acid and subsequentlyimpregnated with a second acid; and passing a gas through the adsorbentmaterial so as to reduce siloxane levels in the gas. In some embodimentsthe first acid and second acid are different acids. The first acid canbe, for example, nitric acid. The second acid generally comprises anacid other than nitric acid. The second acid can comprise, for example,citric acid.

Elements Containing Adsorbent Materials

In reference now to the drawings, FIG. 1 shows simplified view of afilter element for removing contaminants from a gas stream made inaccordance with an implementation of the invention. The element 10includes a bottom 12 and top 14. Gases flow from the bottom 12 throughone or more layers of media pack 16 and then out the top 14 of theelement 10 (as shown by the large arrows depicting general gas flowdirection).

FIGS. 2, 3, and 4 show cross sections of alternative media packconfigurations for elements such as element 10, taken along crosssection A-A′. In FIG. 2 the element 10A has two layers 22, 24 of media.In the depicted embodiments the media layers (such as packed carbonbeds) are substantially equal in volume. The lower layer 24 cancomprise, for example, acid washed activated carbon to primarily removesiloxanes, while the upper layer 22 can contain phosphoric acidimpregnated activated carbon to remove ammonia. Other materials can alsobe included, such as an acid gas remover, which can be blended with theadsorbents in the upper layer 22 and/or lower layer 24.

FIG. 3 shows an element 10B with a similar design to that of FIG. 2, butwith a lower layer 28 containing significantly more media than upperlayer 26. It will be understood that either layer can contain acidwashed adsorbent, and either layer can contain acid impregnatedadsorbent. However, generally a single layer would not contain both acidwashed adsorbent and acid impregnated adsorbent (although such mixturesmight be appropriate for some implementations). Also, it will beunderstood that the upper layer can have more adsorbent than the lowerlayer (and thus the layers 26, 28 can be reversed).

FIG. 4 shows yet another embodiment of a filter element 10C, this timewith three media layers 30, 32, 34. The layers 30, 32, 34 can contain avariety of adsorbents as described herein. For example, they can containone or more of acid washed adsorbents, acid impregnated adsorbents, acidgas removers, or other materials compatible with the reduction ofcontaminants from gases, in particular the reduction of siloxanes.

It will be understood that alternative configurations besides thoseshown in FIGS. 2, 3, and 4 are possible. For example, in someimplementations the various adsorbent materials (such as acid washedcarbon and acid impregnated carbon) can be blended together. In someimplementations the various adsorbent materials are provided in acombination of blends and layered constructions whereby some layers areblended adsorbents, and some layers are non blended adsorbents.

Examples

Efficacy of various materials on the removal of siloxanes and ammoniawas tested using a number of example media constructions. For the tests,air was flowed through an hexamethyldisilazane (HMDS) bubbler togenerate trimethyl siloxane (TMS) and hexamethyldisiloxane (HMDSO) usinga catalyst converter. Total siloxane concentration of the test gas wasmeasured at 20 ppm, with an ammonia concentration measured at 10 partsper million. The gas was maintained at a temperature of 25 degreesCelsius, with a relative humidity of 50 percent. Flow rate of the gaswas maintained so as to simulate a flow rate of 2,600 cubic meters perhour in a full size element. Contaminant levels were measured withFourier transform infrared spectroscopy (FTIR).

The following adsorbent materials were tested, as indicated on FIG. 5and FIG. 6: Carbon A, which was activated carbon with an acid gasremover. Carbon B, which was citric acid impregnated carbon with animpregnation level of approximately 12 to 18 percent. Carbon B1, whichwas citric acid impregnated media with an impregnation level ofapproximately 35 percent. Carbon N, which was nitric acid washed carbon.Carbon N1, which was nitric acid washed carbon at a different mesh size.Carbon P15, which was 15% phosphoric acid impregnated carbon mesh.Carbon P15-1, which was 15% phosphoric acid impregnated carbon mesh.Carbon P10, which was 10% phosphoric acid impregnated carbon mesh.Carbon P10-1, which was 10% phosphoric acid impregnated carbon mesh.Carbon P5, which was 5% phosphoric acid impregnated carbon mesh. CarbonP5-1, which was 5% phosphoric acid impregnated carbon mesh. Carbon NIC,which was non-impregnated carbon. Silica Gel 40, which was a firstsilica gel, and silica Gel 59, which was a second silica gel. Thematerials shown in FIG. 5 and FIG. 6 were composed of materials which,in some instances, were of different mesh.

As is evident from FIG. 5, carbon treated with a nitric acid was showsexcellent performance at removing siloxanes relative to other mediamaterials. As is evident from FIG. 6, a variety of media constructionscan be used for removing ammonia, including phosphoric acid impregnatedcarbon. These materials may be combined, in sequential flow paths, toproduce a filter that removes both siloxanes and ammonia from a gasstream.

FIG. 7 is a chart showing an ammonia removal efficiency curve from a gasstream using adsorbent media, showing two different systems. System Awas made in accordance with the present invention, and included Carbon A& Carbon P15-1 and Carbon N1 & Carbon P15-1. System B contained a firststage Carbon A & Carbon B, plus a second stage of Carbon A & Carbon B.Each system contained substantially the same amount of total carbonmedia. The test conditions were performed at 10 ppmV, 25 degrees C., 50percent relative humidity, and 0.24 second retention time in the system.As shown in FIG. 7, System A performed better than System B in removalefficiency, demonstrating significantly longer effective removal periodsof ammonia.

FIG. 8 is a chart showing hexamethyldisiloxane removal efficiency curvefrom a gas stream using adsorbent media. System A was made in accordancewith the present invention, and included Carbon A & Carbon P15-1 andCarbon N1 & Carbon P15-1. System B contained a first stage Carbon A &Carbon B, plus a second stage of Carbon A & Carbon B. Each systemcontained substantially the same amount of total carbon media. The testconditions were performed at 10 ppmV, 25 degrees C., 50 percent relativehumidity, and 0.24 second retention time in the system. As shown in FIG.8, System A performed better than System B in removal efficiency,demonstrating significantly longer effective removal periods ofhexamethyldisiloxane.

FIG. 9 is a chart showing total a siloxane removal efficiency curve froma gas stream using adsorbent media. System A was made in accordance withthe present invention, and included Carbon A & Carbon P15-1 and CarbonN1 & Carbon P15-1. Each system contained substantially the same amountof total carbon media. System B contained a first stage Carbon A &Carbon B, plus a second stage of Carbon A & Carbon B. The testconditions were performed at 20 ppmV, 25 degrees C., 50 percent relativehumidity, and 0.24 second retention time in the system. As shown in FIG.9, System A performed better than System B in removal efficiency,demonstrating significantly longer effective removal periods of totalsiloxanes.

FIG. 10 is a chart showing a total ammonia removal efficiency curve froma gas stream using adsorbent media. System A was made in accordance withthe present invention, and included Carbon A & Carbon P15-1 and CarbonN1 & Carbon P15-1. Each system contained substantially the same amountof total carbon media. System B contained a first stage Carbon A &Carbon B, plus a second stage of Carbon A & Carbon B. The testconditions were performed at 10 ppmV, 25 degrees C., 50 percent relativehumidity, and 0.24 second retention time in the system. As shown in FIG.10, System A performed better than System B in removal efficiency,demonstrating significantly longer effective removal periods of ammonia.

While the present invention has been described with reference to severalparticular implementations, those skilled in the art will recognize thatmany changes may be made hereto without departing from the spirit andscope of the present invention.

We claim:
 1. A method of reducing siloxane levels in a gas, the methodcomprising: providing a first adsorbent material that has been washedwith an acid; and passing a gas through the adsorbent material so as toreduce siloxane levels in the gas.
 2. The method of any of claims 1 and3-23, wherein the first adsorbent material comprises activated carbon.3. The method of any of claims 1-2 and 4-23, wherein the first adsorbentmaterial is selected from the group silica gel, activated alumina,zeolites, nanoporous supports, and combinations thereof.
 4. The methodof any of claims 1-3 and 5-23, wherein the acid comprises a strong acid.5. The method of any of claims 1-4 and 6-23, wherein the acid comprisesnitric acid.
 6. The method of any of claims 1-5 and 7-23, wherein theadsorbent is washed with an aqueous solution of at least 5 percentnitric acid.
 7. The method of any of claims 1-6 and 8-23, wherein theadsorbent is washed with an aqueous solution of at least 10 percentnitric acid.
 8. The method of any of claims 1-7 and 9-23, wherein thegas passed through the adsorbent material comprises ambient air.
 9. Themethod of any of claims 1-8 and 10-23, wherein the gas passed throughthe adsorbent material is subsequently used for semiconductormanufacturing.
 10. The method of any of claims 1-9 and 11-23, furthercomprising: providing a second adsorbent material; and passing the gasthrough the second adsorbent material.
 11. The method of any of claims1-10 and 12-23, wherein the second adsorbent material comprisesactivated carbon.
 12. The method of any of claims 1-11 and 13-23,wherein the second adsorbent material adsorbent material is selectedfrom the group silica gel, activated alumina, zeolites, nanoporoussupports, and combinations thereof.
 13. The method of any of claims 1-12and 14-23, wherein the second adsorbent material comprises an adsorbentimpregnated with an acid.
 14. The method of any of claims 1-13 and15-23, wherein the acid comprises a strong acid.
 15. The method of anyof claims 1-14 and 16-23, wherein the acid comprises an phosphoric acid.16. The method of any of claims 1-15 and 17-23, wherein the acidcomprises citric acid.
 17. The method of any of claims 1-16 and 18-23,wherein the gas is passed through the first adsorbent material andsubsequently passed through the second adsorbent material.
 18. Themethod of any of claims 1-17 and 19-23, wherein the gas is passedthrough the second adsorbent material and subsequently passed throughthe first adsorbent material.
 19. The method of any of claims 1-18 and20-23, further comprising an acid gas remover.
 20. The method of any ofclaims 1-19 and 21-23, wherein the acid gas remover comprises anadsorbent impregnated a impregnate selected from the group potassiumiodide, potassium carbonate or sodium hydroxide, and combinationsthereof.
 21. The method of any of claims 1-20 and 22-23, wherein theacid gas remover comprises an adsorbent impregnated with potassiumiodide, potassium carbonate, or sodium hydroxide and combinationsthereof.
 22. The method of any of claims 1-21 and 23, wherein the ratioof first adsorbent to acid gas remover is from 2:1 to 1:2.
 23. Themethod of any of claims 1-22, wherein the ratio of first adsorbent toacid gas remover is from 10:1 to 1:10.
 24. A filter element for reducingsiloxane levels in a gas, the filter element comprising: a firstadsorbent material, the first adsorbent material comprising anacid-washed adsorbent; a second adsorbent material, the second adsorbentmaterial comprising an acid-impregnated adsorbent.
 25. The filterelement of any of claims 24 and 26-42, wherein the first adsorbentmaterial comprises activated carbon.
 26. The filter element of any ofclaims 24-25 and 27-42, wherein the first adsorbent material comprisessilica gel.
 27. The filter element of any of claims 24-26 and 28-42,wherein the acid comprises a strong acid.
 28. The filter element of anyof claims 24-27 and 29-42, wherein the acid comprises nitric acid. 29.The filter element of any of claims 24-28 and 30-42, wherein theadsorbent is washed with an aqueous solution of at least 5 percentnitric acid.
 30. The filter element of any of claims 24-29 and 31-42,wherein the adsorbent is washed with an aqueous solution of at least 10percent nitric acid.
 31. The filter element of any of claims 24-30 and32-42, wherein the second adsorbent material comprises activated carbon.32. The filter element of any of claims 24-31 and 33-42, wherein thesecond adsorbent material comprises silica gel.
 33. The filter elementof any of claims 24-32 and 34-42, wherein the acid impregnating thesecond adsorbent material comprises a strong acid.
 34. The method of anyof claims 24-33 and 35-42, wherein the acid impregnating the secondadsorbent material comprises phosphoric acid.
 35. The filter element ofany of claims 24-34 and 36-42, wherein the filter element is configuredfor a gas to first pass through the first adsorbent material andsubsequently pass through the second adsorbent material.
 36. The filterelement of any of claims 24-35 and 37-42, wherein the filter element isconfigured for a gas to first pass through the second adsorbent materialand subsequently pass through the first adsorbent material.
 37. Thefilter element of any of claims 24-36 and 38-42, further comprising anacid gas remover.
 38. The filter element of any of claims 24-37 and39-42, wherein the acid gas remover comprises an adsorbent impregnatedwith potassium iodide, potassium carbonate, and combinations thereof.39. The filter element of any of claims 24-38 and 40-42, wherein theratio of first adsorbent to acid gas remover is from 2:1 to 1:2.
 40. Thefilter element of any of claims 24-39 and 41-42, wherein the ratio offirst adsorbent to acid gas remover is from 3:1 to 1:3.
 41. The filterelement of any of claims 24-40 and 42, wherein at least the firstadsorbent material is provided in a packed bed.
 42. The filter elementof any of claims 24-41, wherein at least the first adsorbent material isprovided in a web form.
 43. A method of reducing siloxane levels in agas, the method comprising: washing an adsorbent material with nitricacid; and impregnating the adsorbent material with a strong acid otherthan nitric acid; and passing a gas through the adsorbent material so asto reduce siloxane levels in the gas.
 44. A filtration system forreducing siloxane levels in a gas, the filtration system comprising: afirst filter element comprising an adsorbent material, the firstadsorbent material comprising an acid-washed adsorbent; a second filterelement comprising an adsorbent material, the second adsorbent materialcomprising an acid-impregnated adsorbent; wherein the filter system isconfigured in a series for a majority of the gas to pass through thefirst filter element and the second filter element.
 45. A filtrationsystem for reducing siloxane levels in a gas, the filtration systemcomprising: a first filter element comprising an adsorbent material, thefirst adsorbent material comprising an acid-impregnated adsorbent; asecond filter element comprising an adsorbent material, the secondadsorbent material comprising an acid-washed adsorbent; wherein thefilter system is configured in a series for a majority of the gas topass through the first filter element and the second filter element. 46.A method of reducing siloxane levels in a gas, the method comprising:providing an adsorbent material that has been washed with an acid; andpassing a gas through the adsorbent material so as to reduce siloxanelevels in the gas.
 47. A method of reducing siloxane levels in a gas,the method comprising: providing an adsorbent material that has beenwashed with a first acid and subsequently impregnated with a secondacid; and passing a gas through the adsorbent material so as to reducesiloxane levels in the gas.
 48. The method of any of claims 47 and49-50, wherein the first acid and second acid are different acids. 49.The method of any of claims 47-48 and 50, wherein the first acidcomprises nitric acid.
 50. The method of any of claims 47-49, whereinthe second acid comprises an acid other than nitric acid.